1. Field of the Invention
The present invention relates to a wafer polishing apparatus which polishes a wafer in the chemical mechanical polishing (CMP) method.
2. Description of the Related Art
U.S. Pat. No. 5,584,751 discloses a wafer polishing apparatus which mainly comprises, as seen from FIG. 5, a wafer holding head 3 having a carrier 1 and a retainer ring 2, and a platen 5 to which a polishing pad 4 is adhered. The wafer polishing apparatus polishes a wafer 6 by pressing the wafer 6 with the carrier 1 against the polishing pad 4 which is rotating, and at the same time presses the retainer ring 2 arranged at an outer periphery of the carrier 1 against the polishing pad 4 so as to surround the periphery of the wafer 6, thereby preventing the wafer 6 from slipping out of the carrier 1.
The material of the polishing pad 4 is selected either a hard type or soft type depending on the material (such as SiO2) of the polished layer (insulator film) of the wafer. When the polishing pad 4 of the soft type is used, a part along the periphery of the polishing pad 4 which contacts with the retainer ring 2 is waved (so-called waving occurs on the polishing pad 4). If the waving occurs on the polishing pad 4, an outer periphery 6A of the wafer 6 is excessively polished by a wavily deformed part 4C of the polishing pad 4, and the wafer 6 is not uniformly polished.
The waving occurs specifically in parts 4A and 4B which contact with an outer periphery 2A and an inner periphery 2B of the retainer ring 2 positioned at an upstream in a rotation direction of the polishing pad 4, and also in a part 4C which contacts with an inner periphery 2C of the retainer ring 2 positioned at a downstream in the rotation direction of the polishing pad 4. Although the parts 4A and 4B do not cause problems since they are away from the outer periphery 6A of the wafer 6, the part 4C at the inner periphery 2C is excessively polished because the outer periphery 6A of the wafer 6 contacts with the wavily deformed part 4C.
In order to cope with the problem, the wafer polishing apparatus of U.S. Pat. No. 5,584,751 prevents the waving and the excessive polishing of the outer periphery 6A of the wafer 6 by lowering a pushing force of the retainer ring 2 against the polishing pad 4.
However, the wafer polishing apparatus cannot perfectly eliminate the waving.
The polishing pad surrounded by the retainer ring keeps its flatness by being pressed by the retainer ring and elastically deformed. Thus, the contact force of the retainer ring is set to be the same as a restoring force of the polishing pad. If the contact force of the retainer ring is lowered as described above, the restoring force of the polishing pad becomes larger than the pushing force of the retainer ring. The polishing pad is thus wavily deformed along the outer periphery of the wafer, and the outer periphery of the wafer is excessively polished.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a wafer polishing apparatus which can uniformly polish the entire surface of the wafer by preventing the excessive polishing of an outer periphery of the wafer.
In order to achieve the above-described object, the present invention is directed to a wafer polishing apparatus which polishes a surface of a wafer, comprising: a carrier that holds the wafer and presses the surface of the wafer against a polishing pad that is rotating; and a retainer ring which is arranged at an outer periphery of the carrier to surround the periphery of the wafer and is pushed against the polishing pad, the retainer ring having a step part on a face that contacts with the polishing pad so that a wavily deformed part of the polishing pad enters the step part.
In order to achieve the above-described object, the present invention is directed to a wafer polishing apparatus which polishes a surface of a wafer, comprising: a carrier that holds the wafer; a first pressing device that presses the carrier against a polishing pad that is rotating; a pressurized air layer forming device that forms a pressurized air layer between the carrier and the wafer and transmits a pressing force from the first pressing device to the wafer through the pressurized air layer; a retainer ring which is arranged at an outer periphery of the carrier to surround the periphery of the wafer and is pushed against the polishing pad, the retainer ring having a step part on a face that contacts with the polishing pad so that a wavily deformed part of the polishing pad enters the step part; and a second pressing device that presses the retainer ring against the polishing pad.
The invention relates to a wafer polishing apparatus which presses the wafer against the polishing pad with the carrier to polish the wafer. The invention relates to a wafer polishing apparatus which presses the wafer against the polishing pad with the carrier to polish the wafer by forming the pressurized air layer between the carrier and the wafer and transmitting the pressing force to the wafer through the pressurized air layer. The present invention provides a step part to the retainer ring of the wafer polishing apparatus so that the wavily deformed part of the polishing pad enters the step part.
By the above-described structure, the wavily deformed part caused by the waving of the polishing pad occurs away from the outer periphery of the wafer. Therefore, the present invention prevents the excessive polishing of the outer periphery of the wafer without suppressing occurrence of the waving, and thus can uniformly polish the entire surface of the wafer.